Each year there are hundreds of millions of cases involving diseases that are transmitted by insects and/or arachnids. These diseases result in millions of annual fatalities in addition to having a massive impact on health care resources throughout the world. For example, most orders of ticks include species of medical importance. While blood-sucking ticks can cause irritation and malaise in the host, the tick's role as carrier and transmitter of human disease organisms is of substantial medical concern. The disease organisms, which include but are not limited to viruses, rickettsiae, and spirochaeta bacteria, are transmitted through the tick's saliva during feeding. Tick-borne viruses can cause hemorrhagic fevers, encephalitis, and Lyme disease (LD), the latter of which is a multisystem inflammatory disease that can affect the skin and joints, nervous system, and other organic systems. Like a virus, rickettsia can develop only inside living cells. The main rickettsial infections observed in humans are the spotted fevers such as Rocky Mountain spotted fever, tick-bite fevers, and tick-typhus fevers. The condition known as Epizootic Bovine Abortion (EBA) has been associated with blood feeding by the soft tick Ornithodoros coriaceus, and causes in excess of $30 million in damage in the state of California alone, with losses in particularly bad years approaching $100 million. Another disease vector affecting cattle is a soft tick that serves as a vector for numerous arboviruses.
Larval mites of the family Trombiculidae, commonly called chiggers or red bugs, can cause a dermatitis (scrub-itch) that results from an allergic reaction to the chigger's saliva and can also transmit human disease organisms. The most common mites that infect humans are scabies or itch mites, which are also known to be severe irritants to cattle. Additional pests that have been shown to cause diseases or other conditions include house dust mites, which induce allergic reactions in the form of asthma and rhinitis in humans; food mites, which cause dermatitis in people handling infested food; and the crab louse, which causes discomfort to humans but can also act as a vector for exanthematous typhus, a disease caused by Rickettsia prowazekii that has caused millions of deaths
Perhaps the most well known insect vectors for disease are the various types of mosquitoes. Mosquitoes are particularly adept at transmitting diseases caused by viruses, but can also carry disease-causing nematodes and protozoans. The mosquitos most closely associated with human disease are those of the genus Aedes. In terms of human health problems, the most important species of Aedes is Aedes aegypti, which is a vector for the virus that causes yellow fever in humans. Other viruses associated with the Aedes species include those that cause dengue fever, various forms of encephalitis, hemorrhagic fever, and yellow fever. Additionally, the common house mosquito, Culex pipiens, has been is implicated in the transmission of various forms of encephalitis and the filarial worms Wuchereria banufti or Brugia malayi, which is responsible for elephantiasis. Mosquitoes might also be a vector for Ebolavirus, a filovirus that causes a hemorrhagic fever that is frequently fatal. The mosquito genus Anopheles can also act as vectors for pathogenic organisms that circulate in the bloodstream such as members of the protozoan genus Plasmodium, which cause malaria in between 200 and 300 million people and which kill at least two million every year.
And finally, cockroaches can also transmit disease. Cockroaches of various species can be found in grocery stores, restaurants, hospitals, jails, hotels, apartments, homes, and in most any place where food is stored. The droppings and skin of cockroaches can cause hives or rashes, coughing, sneezing, and other contact and/or inhalant allergic reactions in humans. The prodigious ability of cockroaches to multiply, along with their close association with people and food and their tendency to hide in places that are difficult to access, make it difficult to successfully exterminate them.
As a result, tremendous efforts have been made to better understand the mechanisms that underlie host attraction, feeding, and other behaviors of insect species that can serve as vectors for diseases or other undesirable conditions in humans and other susceptible hosts. Such knowledge would allow for the design of strategies for intervening in the process by which pathogenic vectors spread disease.
What are needed, then, are new methods and compositions that can be employed in screening for agents that modulate insect and/or arachnid behavior, and in some cases, screening for agents that can act as repellents and even as pesticides for insects and/or arachnids.